The present invention generally relates to hand held guns used for mixing and dispensing reactive chemical foam compositions, such as curable polyurethane foams. More particularly, it relates to a new and improved dispenser gun and dispenser module including valving elements which may be selectively compression loaded to provide improved sealing and dispensing performance and extended module service life.
Reactive chemical foam compositions, such as curable polyurethane foams, are presently well known and used in a number of different applications. The curable foam compositions typically comprise a two-part composition and, in the case of polyurethane foams, one part of the composition includes a polyol component and the other part includes an isocyanate component. Chemical foaming agents, curing agents, catalysts or accelerators, as well as other modifying additives, may be incorporated in one or both of the component parts. These two-parts of the foaming composition are separately stored in different containers until use.
For use, the two parts of the composition are rapidly mixed together. A rapid cross linking reaction and foam expansion commences which ultimately yields a resilient, low density, but relatively high load bearing urethane rigid foam. Expanding chemical foams are useful in such applications as thermal insulation, in floatation, in coatings and, more recently, the foams have been used in the specialty packaging industry.
According to present practice, the urethane components including the resin or polyol component and the isocyanate component are stored under pressure in containers which are attached to a hand held discharge gun by means of various hoses and couplings. The gun includes a trigger operated dispenser valve designed to permit the two-parts of the composition to flow through the hoses and into a mixing chamber wherein the products are rapidly mixed to form a reactive and expanding chemical foam composition which exits through a foam discharge nozzle or opening.
In these dispensing guns, the components are mixed by direct or indirect impingement with each other under conditions of high pressure to ensure thorough mixing. The design of the discharge valves and nozzles has become a matter of concern in the art. The component parts of the foam composition are highly chemically reactive and begin to form cured polymeric products within a matter of seconds. Premature leaking and mixing of the components within the dispensing nozzles is a serious and major concern because leakage results in undesirable curing in the nozzle causing blockage and damage to the nozzles in use. As a result, the nozzles have to be frequently replaced at considerable expense. Providing adequate seals within the nozzle assemblies in the high pressure environment has been another major problem to those in the art.
Prior art foam dispensing guns are known, for example from U.S. Pat. No. 4,469,251, U.S. Pat. No. 4,568,003 and from U.S. Pat. No. 4,993,596. In accordance with these prior dispensing gun arrangements, a detachable dispensing module includes a mixing chamber defined in a central bore within a polymeric insert. Typically, the polymeric insert is formed of a TEFLON.RTM. material because the reactive foam composition and its components are not adherent to the TEFLON.RTM. surfaces along the interior of the bore.
More particularly, the TEFLON.RTM. insert has a central bore extending longitudinally therethrough. A plurality of openings extend through a sidewall of the insert in communication with the bore for supplying the organic resin and the isocyanate components into the mixing chamber. A valving rod is provided in a slidable interference fit within the bore to control the flow of organic polyol resin component and isocyanate component from the side openings into the mixing chamber and discharge of the foam therefrom. Although the inserts exhibit non-adherent surface characteristics, TEFLON.RTM. materials are notorious for suffering from hysteresis or cold flow dimensional instability. Cold flow of the TEFLON.RTM. material causes a distortion or a change in the critical dimensions of the central bore and the side openings of the insert. Over time this often results in a loss of the interference fit between the valving rod and the insert. As a result, the ability of the valving rod to effectively seal the openings to thereby prevent leakage of the reactive components into the mixing chamber is lost. Leakage ultimately causes obstruction within the mixing chamber which renders the dispensing module generally inoperable.
In an effort to overcome the tendency of the valving inserts to undergo cold flow deformation with a consequent loss in sealing and usefulness, conventional dispenser cartridges or modules have been provided with means for applying a constant axial and radial compressive load against polymeric insert member. Applying a constant radial and axial loads on the insert tends to reduce some of the cold flow induced failures of the prior art nozzles. Applying a constant radial and axial load increases frictional forces developed between the valve insert and the valving rod which tends to increase the residual stresses on the insert responsible for cold forming. Presently, the frequency of failure is still undesirably high in view of the expense associated with replacement and repair of the mixing chamber/dispensing modules.
Accordingly, to overcome the disadvantages of the prior art dispensing guns, it is an object of the present invention to provide a new and improved foam dispensing gun including a dispenser module characterized by prolonged or extended use lives.
It is another object of the present invention to provide a foam dispensing gun including a new and improved dispensing module which applies a compressive load against the polymeric valving insert in a critical seal area.
It is a further object of the present invention to provide a new and improved dispenser module for use in foam dispenser guns having a compression loaded polymeric insert designed to permit relaxation of the polymeric insert in a controlled manner so that cold flow deformations should they occur, occur outside the critical seal area.
It is another object of the present invention to provide a new and improved dispenser gun for foam compositions including a dispenser module adapted to receive a foam discharge guide member in the form of a tube or hose extension received over the discharge nozzle for re-directing discharged foam away from the gun to a desired target location.
It is still a further object of the present invention to provide a new and improved dispenser module for a foam dispensing gun adapted to receive a forward foam discharge guide including means for introducing a blast of air under pressure into the discharge guide behind a slug of dispensed foam to urge substantially all of the dispensed foam out of the discharge guide, to thereby purge the guide for the next shot of dispensed foam.